1. Field of the Invention
The present invention generally relates to the field of industrial production of aluminum alloys, and more particularly the field of industrial production of aluminum metal matrix nanocomposites
2. Description of the Prior Art
Currently 2000, 4000 and 6000 series aluminum alloys are widely used for lightweight structural applications that do not require high material strength and high specific stiffness or modulus. Highly loaded structural applications produced from aluminum alloys typically use 7000 series alloys. Aluminum alloys in the 7000 series are also more difficult to form into final products than competing 2000 and 6000 series aluminum alloys.
Particularly, Micro Ceramic Particulate Reinforced Aluminum Matrix Composites (MCP-AMCs) have been used in the aerospace industry and other areas due to their high specific stiffness. Aluminum oxide, boron carbide and silicon carbide micro size powders are the most common reinforcements. The specific stiffness increase is dictated by the properties of the ceramic used. Boron carbide has the highest elastic modulus and the lowest density of these reinforcements.
Silicon carbide, which has a slightly lower elastic modulus and higher density than boron carbide, yields a MCP-AMC with intermediate properties. Aluminum oxide has the highest density and the lowest modulus among the three ceramics. Therefore, Al2O3 reinforce aluminum possesses the lowest specific properties.
The strength of a MCP-AMC is mainly determined by the strength of the aluminum matrix alloy. The strength of a MCP-AMC using a 6000 series aluminum alloy matrix is not as high as the strength of 7000 series aluminum. For example, 15 volume % SiC reinforced 6061 aluminum has a yield strength of 58 ksi., which is lower than the 62 ksi. for 7075-T76 aluminum alloy.
It has been shown that Nano Ceramic Particulate Reinforced Aluminum Matrix Composites (NCP-AMCs) have higher strength than that of MCP-AMCs. Uniformly distributed nano-scale ceramic particles in an aluminum matrix enhance the strength of the resultant composite. For example, a uniform distribution of about 0.5 volume % of nano-scale aluminum oxide in 6092 aluminum increases the strength of the NCP-AMC about 10%. The same amount of micro ceramic powder uniformly distributed in a pure aluminum alloy has no effect to the strength.
U.S. patent application Ser. No. 10/738,275 by Peng et al. disclosed how to produce nano aluminum oxide reinforced aluminum matrix composites, which can have up to about 45 vol. % nano phase Al2O3 reinforcement. However, the specific stiffness or specific modulus of such nano aluminum composite is lower than that of a micro B4C or SiC powder reinforced aluminum matrix composite.